Magento 1.9.0.1 Cart Empty After Login at Checkout – Safari Browser Issue

Use an event observer to empty cart on customer login.

config.xml

<customer_login>
  <observers>
      <foo_bar> <!-- foo_bar should be unique tag for within all customer_login observers-->
          <class>foo_bar/observer</class>
          <method>customerLogin</method>
          <type>singleton</type>
      </foo_bar>
  </observers>
</customer_login>

Observer

class Foo_Bar_Model_Observer {
    public function customerLogin(Varien_Event_Observer $observer) {
        foreach( Mage::getSingleton('checkout/session')->getQuote()->getItemsCollection() as $item ) {
            Mage::getSingleton('checkout/cart')->removeItem( $item->getId() )->save();
        }
    }
}

This is default behavior for Magento as is.

We solved this by installing this extension: https://github.com/jacquesbh/jbh_cartmerge

It has option to turn on/off merging of carts, also to enforce mergen when the cart is empty

Should be default setting in Magento ...